In a medium skillet over medium heat, melt butter Add apples and onion Cover and cook, stirring frequently, until apples are almost tender, 3 to 4 minutes Meanwhile, in a small bowl, whisk together cornstarch, sugar, salt and pepper Stir in 2⁄3 cup water Stir water mixture and ½ cup of the blueberries into the apples Cook, stirring gently, until thickened and sauce begins to color, 1 to 3 minutes Remove from heat, stir in lemon juice and remaining ½ cup of blueberries Serve with sliced pork or ham, chicken, turkey or game